1. Field of the Invention
The invention relates to a driving device for an electric lock latch, and more particularly to a structure with a drive shaft having an external threaded for driving an unequal diameter spiral spring in threaded connection thereto. Moreover, the lock latch is connected at the external part of the spiral spring. As a result, the circular motion of the drive shaft is converted into the rectilinear motion of the spiral spring such that the lock latch is moved. In this way, the locked and unlocked state of the lock device may be changed by the movement of the lock latch. Moreover, the structure of the invention can be applied to all kinds of lock devices.
2. Description of the Related Art
It is quite normal that the lock employs an electromagnetic valve to control the movement of the latch, thereby changing the locked or unlocked state. Such a structure is disclosed in the U.S. Pat. No. 6,082,791. However, the activation of the electromagnetic valve requires a large power consumption. Therefore, it is necessary to provide an external power source and a control unit for the electric lock latch using the electromagnetic valve. As a result, the installer must have the electronic knowledge and the installation skill, thereby causing much difficulty for the installer.
In order to move the lock latch via the electromagnetic valve, a motor may be used to impart a motion to the lock latch. U.S. Pat. No. 5,697,798 “MOTORIZED LOCK ACTUATORS”, U.S. Pat. No. 5,628,216 “LOCKING DEVICE” and U.S. Pat. No. 6,076,870 belong to such a structure. “Motorized electric strike” disclosed in U.S. Pat. No. 6,076,870 relates to an electric strike with a pivoting locking member for locking an electric strike in the closed position. The locking member is pivoted between the locked and unlocked positions by a low current motor. A drive pin pivotally engages the locking member. The motor rotates a roll pin threadably engaging the coil faces of a spring mounted to the drive pin. Rotation of the motor compresses or expands the spring to axially move the drive pin and thereby pivot the locking member between the locked and unlocked positions.
However, the structure according to the U.S. Pat. No. 6,076,870 employs a motor to impart a rotary motion to the roll pin, thereby biasing the spring in a retracted or extended position. In this way, the drive pin is axially moved to bring the locking member between the locked and unlocked positions. The spring is equidimensionally formed. The time to supply power to the motor must be exactly controlled to prevent the breakdown of the spring due to over-compression or over-extension when the spring is moved by the rotation of the roll pin. Moreover, the installation of the roll pin and the drive pin according to the U.S. Pat. No. 6,076,870 is complicated. Therefore, a further improvement is required.
With reference to FIGS. 1A and 1B, U.S. Pat. No. 5,628,216 discloses a lucking device comprising a spring 60 being fixed to a guide member 62 at one end such that the spring 60 rotates with the shaft of a gear head 63 and, thus, with the shaft of a motor 67. During rotation of the motor shaft in a first direction, a pin 110 engages the free end of the spring 60 such that a plug 58 moves towards a motor 67 placing a locking device 10 in the locked position. Moving the motor shaft in a second direction opposite the first direction, the pin 110 engages the free end of spring 60 such that the plug 58 moves away from the motor 67, placing the locking device. The prior invention is quiet as to the diametric proportion of the spring 60. However, the shape of the spring 60 can be inferred from FIG. 1A and it illustrates spring 60 having a constant diametric proportion. Moreover, the first end of spring 60 is fixed to guide member 62.
Based on the features disclosed in U.S. Pat. No. 5,628,216, the spring 60 rotates with the shaft of a motor 67, such that the spring 60 may be excessively compressed or may be excessively extended, resulting in an elastic fatigue and a high breakdown.